Process for the production of macrocyclic esters and lactones utilizing double metal salt catalysts

ABSTRACT

A process is provided for the thermal depolymerization of polyesters to produce macrocyclic compounds utilizing mixed-metal catalysts. Useful mixed-metal catalysts consist of an aluminum alkoxide or aluminum carboxylate with an alkali metal or magnesium alkoxide or carboxylate, or double metal salts thereof. High yields and enhanced rates of reaction are obtained using the mixed-metal catalysts of this invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 285,727 filedJuly 22, 1981 and issued on July 12, 1983 as U.S. Pat. No. 4,393,223,which is a continuation-in-part of abandoned application Ser. No.073,755 filed Sept. 10, 1979.

BACKGROUND OF THE INVENTION

Lactones and cyclic esters are obtained by the thermal depolymerizationof the corresponding linear polyesters accompanied by ring closure. Forsuch processes, the polyester is heated at an elevated temperature inthe presence of a catalyst. The reaction is carried out under reducedpressure and the macrocyclic compound and other volatile products formedduring the course of the depolymerization are removed from the reactionzone as they are formed. Due to the poor heat transfer within the highlyviscous reaction mass, until recently it was only possible to conductthe reaction as a batch-type operation--thus severely limiting thecommercial utility of the process. With the discovery of the process ofU.S. Pat. No. 4,165,321, however, the continuous and semi-continuousproduction of macrocyclic compounds by thermolysis of polyester is nowpossible.

Chlorides, nitrates, carbonates and oxides of magnesium, manganese,iron, cobalt and tin (all in the divalent state) are disclosed to beeffective catalysts for the batch depolymerization of linear polyestersin U.S. Pat. No. 2,092,031. For the process of U.S. Pat. No. 4,165,321Lewis metal salts such as the oxides, hydroxides, halides, orcarboxylates, of Group IIIa, IVa, IVb, Va, VIIb and VIII metals areindicated to be useful catalysts. Yasakawa et al. reported the use oflead catalysts (oxide, hydroxide, carbonate, nitrate, borate or organicacid salts) for the preparation of large ring lactones via thermaldepolymerization in Chemical Abstracts, Vol. 78 (1973), 158966q and158968s. Cyclic esters are also obtained via thermal degradation ofpolyesters using SnCl₂.2H₂ O (Chemical Abstracts Vol. 86 (1977),156163s) and in U.S. Pat. Nos. 4,105,672; 4,136,098; and 4,157,330 a tincarboxylate or an organotin compound in conjunction with anO,O-dialkyl-(3,5-di-t-butyl-4-hydroxy-benzyl)phosphonate is employed tocatalyze the reaction. In somewhat related procedures, cyclic esteranhydrides of α-hydroxycarboxylic acids are formed in vacuo bydepolymerizing the corresponding linear polymer at 200°-240° C. in thepresence of lead (II) stearate (British Pat. No. 1,108,720).

While all of the aforementioned metal compounds catalyze thedepolymerization and ring closure to varying extents, whether theprocess is conducted as a batch or continuous operation, they are notwithout certain disadvantages. In the first place, many of thesecatalysts are insoluble or have limited solubility in the reactionmedium and give poor yields of the desired macrocyclic products. Evenwhen acceptable yields are obtained the rates of reaction are oftenslower than desirable so that process equipment can be utilized at onlya fraction of its capacity. Efforts to increase the reaction rate byraising the temperature of reaction are only partially successful sincethis often leads to destructive thermal decomposition and/or excessivefoaming, particularly in batch-type operations.

Additionally, it is virtually impossible to completely eliminate thepresence of some heavy metal contaminants in the macrocyclic product.The presence of even trace amounts of heavy metal residues can impartundesirable discoloration to the product and, if the product is stored,may promote degradation of the macrocyclic compound or other componentsformulated therewith. An even more serious problem exists when thecatalyst is derived from a toxic metal, such as lead. Toxic metalcontaminants cannot be tolerated in most applications where macrocycliccompounds are utilized and this either precludes the use of the productsin these application areas or makes it necessary to subject themacrocyclic product to costly and time consuming post-treatmentoperation(s) capable of eliminating the metal residue.

Aluminum oxide has been used for depolymerizations carried out atatmospheric pressure using superheated steam (Czech Pat. No. 108,726)and the use of aluminum is reported in Japanese Pat. No. Sho35(1961)-1375 for the thermal depolymerization of polyesters to formcyclic esters and lactones. Aluminum alkoxides derived from simplealcohols are used for the preparation of large-ring lactones andlarge-ring ethylene dioates in Japan No. 72 25,071 and Japan KokaiTokkyo Koho No. 79,115,390, respectively.

SUMMARY OF THE INVENTION

This invention relates to an improved process whereby it is possible toobtain macrocyclic compounds, including esters, ether-esters, lactonesand ether-lactones in good yield by the thermal depolymerization ofpolyesters utilizing mixed metal catalysts. Furthermore, it has beenobserved that by the use of these mixed metal catalysts rates ofreaction are significantly increased and it is possible to conduct thereaction at higher temperatures than was heretofore possible. By theprocess of this invention it is also possible to conveniently andeconomically obtain macrocyclic compounds which are completely free oftroublesome heavy metal residues.

For the present improved process a linear polyester is heated at atemperature in the range 200° C. to 400° C. under reduced pressure inthe presence of a mixed metal catalyst comprised of an aluminum alkoxideor aluminum carboxylate and an alkoxide or carboxylate of lithium,sodium, potassium or magnesium. Typically the depolymerization iscarried out at a pressure from about 10 mm Hg to 0.01 mm Hg and thecatalyst is present in an amount from about 0.01 to 20 weight percent,based on the polyester. The resulting cyclic esters, cyclicether-esters, lactones and ether-lactones will have from 8 to 20 carbonatoms.

Aluminum alkoxides useful for the invention are derived fromconventional monofunctional branched- or straight-chain alcohols oralkoxyalcohols and have the formula Al--O--C_(m) H_(2m) --R₁ ]₃ where mis an integer from 1 to 22 and R₁ is hydrogen or an alkoxy or polyalkoxygroup having 1 to 16 carbons. The carboxylates of aluminum have theformula ##STR1## where R₂ is a C₂₋₂₂ alkyl (saturated or containingunsaturation), phenyl or substituted-phenyl having 7 to 20 carbon atoms.

Especially useful catalysts of this invention are mixed metal catalystsobtained when the aluminum alkoxide or aluminum carboxylate is combinedwith the alkali metal or magnesium alkoxide or carboxylate. The alkoxideand carboxylate moieties of the alkali metal or magnesium can be thesame or different as that of the aluminum. Up to about 10 moles alkalimetal or magnesium compound can be used per mole of the aluminumcomponent, however, the molar ratio will more usually range from 0.05:1to 8:1. Mixed metal catalysts obtained from alkoxides or carboxylates oflithium, sodium and potassium are particularly desirable.

The components of the mixed metal catalyst may be added individually tothe reactor or the components can be reacted and the resulting doublemetal salts employed. Useful double metal salts obtained by reacting thealuminum alkoxide or carboxylate and alkali metal compound correspond tothe general formula

    AlM.sub.a (OC.sub.m H.sub.2m R.sub.1).sub.b (OOCR.sub.2).sub.c

where m, R₁ and R₂ are the same as defined above, M represents thealkali metal, a is an integer from 1 to 3, b and c are integers from 0to 6 and b+c=a+3.

DETAILED DESCRIPTION

The present invention relates to an improvement in the process for thedepolymerization of linear polyesters accompanied by ring closure toform macrocyclic esters and lactones having from 8 to 20 atoms in thering, said improvement comprising the use of an aluminum alkoxide oraluminum carboxylate mixed metal catalyst.

Thermal depolymerization reactions are well known and in this regardreference may be had to the references previously referred to. Thermaldepolymerization of polyesters is typically accomplished at temperaturesin the range 200° C. to 400° C. and, more usually, in the range 250° C.to 360° C. Subatmospheric pressures are employed to facilitate removalof the macrocyclic products. The pressure will generally be less thanabout 50 mm Hg and, most preferably, will range from about 10 mm Hg to0.01 mm Hg. The temperature and pressure employed for the reaction willvary depending on the particular polyester to be depolymerized, themanner of operation and design of the process equipment.

Polyesters useful in these depolymerization processes are obtained byconventional methods known to the art. If cyclic esters and ether-estersare to be produced the polyester will have the formula ##STR2## where R'represents a bivalent hydrocarbon radical of a dicarboxylic acid, R"represents a bivalent hydrocarbon radical of a diol, x is 1 in the caseof cyclic esters and greater than 1 for cyclic ether-esters, and nrepresents the number of repeating units in the polyester, i.e., degreeof polymerization. For the production of lactones and ether-lactones thepolyesters will have the respective formulae ##STR3## where R", x and nare the same as above, R"' represents a bivalent hydrocarbon radical andA is an oxygen or sulfur atom. The above formulae indicate the recurringunits present in the linear polyester without regard to terminal groups.It is advantageous to use polyesters which are terminated withmonocarboxylic acid(s) and/or monofunctional alcohol(s) to control themolecular weight and viscosity of the polymer. Polyesters having acidvalues and hydroxyl values less than about 20 and, more usually, lessthan 10 are particularly useful. The degree of polymerization of thepolyesters will generally be between about 5 and 150.

The polyesters are derived from conventional dicarboxylic acids, diolsand hydroxymonocarboxylic acids. Preferably these reactants arealiphatic and may be saturated or contain olefinic unsaturation and canbe branched- or straight-chain. Aromatic or alicyclic dicarboxylic acidswill contain from 3 up to about 18 carbon atoms and more preferablythese acids will have from about 8 to 14 carbon atoms. Usefuldicarboxylic acids include, for example, malonic acid, maleic acid,succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid,sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid,pentadecanedioic acid, and the like. Mixtures of two or moredicarboxylic acids may also be employed. Polyesters derived fromalicyclic acids such as cyclohexane-1,4-dicarboxylic acid and1,3-cyclohexadiene-1,4-dicarboxylic acid may also be used. C₉₋₁₃saturated aliphatic dicarboxylic acids are especially preferred sincemacrocyclic compounds derived therefrom exhibit especially desirablefragrance properties which make them useful in a wide variety ofcosmetic applications.

Hydroxymonocarboxylic acids used for the preparation of polyestersinclude 15-hydroxypentadecanoic acid, 16-hydroxyhexadecanoic acid,10-oxa-16-hydroxyhexadecanoic acid, 11-oxa-16-hydroxyhexadecanoic acid,12-oxa-16-hydroxyhexadecanoic acid, 10-thia-16-hydroxyhexadecanoic acid,11-thia-16-hydroxyhexadecanoic acid, 12-thia-16-hydroxyhexadecanoicacid, and the like.

Diols from which useful polyesters are typically derived by reactionwith the aforementioned dicarboxylic acids are primarily aliphatic diolshaving from 2 to 12, and more preferably, 2 to 6 carbon atoms. The diolsare preferably saturated and can be either straight-chain or branched.Useful diols include ethylene glycol, 1,2- or 1,3-propanediol, 1,2-,1,3-, or 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol,2,3-dimethyl-2,3-butanediol, 1,8-octanediol, 2-ethylhexanediol,1,10-decanediol, 1,12-dodecanediol, diethylene glycol, triethyleneglycol, tetraethylene glycol, and the like. Alicyclic diols such as1,4-cyclohexadimethanol may also be employed. Polyesters derived fromethylene glycol and di-, tri- and tetraethylene glycol are especiallyadvantageous for use in depolymerization processes of this type.

Employing polyesters of the above types in the process of thisinvention, it is possible to obtain cyclic esters, cyclic ether-esters,lactones and ether-lactones having from 8 to 20 carbon atoms in thering. The cyclic esters and ether-esters will have the general formula##STR4## where R' is a bivalent aliphatic hydrocarbon radical, which canbe branched- or straight-chain, saturated or contain unsaturation,having from 1 to 16 carbon atoms, R" is a saturated bivalent aliphatichydrocarbon radical having 2 to 12 carbon atoms and x is an integer from1 to 4. Especially useful cyclic esters and ether-esters are those wherethe moiety R' is a saturated radical having from 3 to 12 carbon atoms,the radical R" has 2 to 6 carbon atoms, and x is 1 or 2. Lactones andether-lactones obtained by the present improved process from polyestersof the above-identified types will have the formula ##STR5## wherein R"'represents a bivalent aliphatic hydrocarbon radical having from 6 to 18carbon atoms, R" represents a saturated bivalent aliphatic hydrocarbonradical having 2 to 12 carbon atoms, A is oxygen or sulfur, and x is aninteger from 1 to 4. Preferred lactones and ether-lactones are thosewhere R"' is a saturated bivalent aliphatic hydrocarbon radical havingfrom 10 to 14 carbon atoms, R" contains from 2 to 6 carbon atoms, A isoxygen, and x is 1 or 2.

Illustrative macrocyclic esters and ether-esters which can be producedin accordance with the depolymerization process of this inventioninclude: 3,6,9-tridecamethylene malonate, dodecamethylene malonate,decamethylene malonate, ethylene suberate, ethylene azelate,3-oxa-pentamethylene azelate, 3-methylpentamethylene sebacate, ethyleneundecanedioate, ethylene dodecanedioate, ethylene brassylate,ethylene-α-methylbrassylate, ethylene-α,α-dimethylbrassylate,ethylene-α-ethylbrassylate, and the like. In addition to theaforementioned products still other cyclic compounds such astetradecamethylene carbonate, dodecamethylene oxalate and7-oxa-tridecamethylene oxalate and bicyclic and polycyclic materialssuch as hexamethylene, tetra- (or hexa-) hydrophthalate can be obtainedby the process of this invention. Exemplary lactones and ether-lactonescorresponding to the above formulae include: pentadecanolide,12-oxa-pentadecanolide, 12-thia-pentadecanolide, hexadecanolide,10-oxa-hexadecanolide, 11-oxa-hexadecanolide, 11-thia-hexadecanolide and12-oxa-hexadecanolide.

The improvement of this invention for the depolymerization of polyestersconsists of the use of specific mixed metal catalysts wherein one of themetals is aluminum. Aluminum alkoxides and carboxylates are employed toobtain the mixed metal catalysts. While these aluminum compounds areeffective catalysts by themselves for the thermal depolymerization andring closure reaction, it has quite unexpectedly been discovered thatimproved results are obtained if an alkali metal or magnesium alkoxideor carboxylate is employed therewith or reacted with the aluminumcompound to form a double metal salt. Such catalytic systems obtainedfrom aluminum alkoxides or aluminum carboxylates with alkoxides orcarboxylates of lithium, sodium, potassium or magnesium are referred tohereinafter as mixed metal or plural metal catalysts and areparticularly effective depolymerization catalysts.

Rapid reaction rates and high yields of the desired macrocyclic productare obtained by the process of this invention. In addition to theseadvantages, the use of troublesome heavy metals is avoided by the use ofthe mixed metal catalysts and the process can be carried out at highertemperatures than was heretofore considered possible with minimalthermal decomposition. The amount of catalyst employed for thedepolymerization reaction will generally range from about 0.01 to about20 percent by weight, based on the polyester. While even largerquantities of catalyst can be utilized, any advantage realized therebyis generally offset by the additional cost involved. Most usually themixed metal catalyst will be present in an amount from 0.1 to 10 weightpercent.

Aluminum alkoxides and carboxylates used to obtain the mixed metalcatalysts of this invention have the respective formulae ##STR6## wherem is an integer from 1 to 22, R₁ is hydrogen, an alkoxy or polyalkoxyradical having from 1 to 16 carbon atoms, and R₂ is an alkyl grouphaving from 2 to 22 carbon atoms and which can be saturated or containunsaturation, phenyl or substituted-phenyl having from 7 to 20 carbonatoms. Especially useful alkoxides and carboxylates are those wherein mis an integer from 2 to 12 and R₁ is hydrogen, methoxy, ethoxy or di-,tri-, or tetraethoxy, and wherein R₂ is a C₈₋₁₈ alkyl group, phenyl, ora substituted phenyl wherein the substituent is an alkyl, alkoxy orpolyalkoxy group. The alkoxides and carboxylates of aluminum may beemployed individually or a mixture of two or more of these compounds canbe used. Furthermore, these compounds may be added to the reactor assuch or generated in the reaction environment. For example, the aluminummay be introduced as an enolate, such as isopropoxy aluminumacetoacetonate, and the chelating group displaced by alkoxide and/orcarboxylate groups.

While the above-defined aluminum alkoxides and aluminum carboxylates areuseful catalysts for the thermal depolymerization of polyesters toproduce macrocyclic compounds, it has quite unexpectedly been discoveredthat catalytic activity is significantly enhanced if an amount rangingup to about 10 moles of an alkali metal or magnesium alkoxide orcarboxylate is present per mole aluminum compound. Highly effectivemixed metal catalysts capable of giving very rapid rates ofdepolymerization are obtained when from 0.05 to 8 moles alkali metal ormagnesium compound is present per mole aluminum compound. Especiallyuseful catalysts are those wherein from about 0.1 to 3 moles of acarboxylate or alkoxide of lithium, sodium or potassium is present permole aluminum alkoxide or carboxylate.

Useful alkoxides and carboxylates of alkali metals or magnesium will beof the same type as described above for the aluminum compounds. In otherwords these compounds will correspond to the formulae ##STR7## where Mis lithium, sodium, potassium or magnesium, y is 1 when M is lithium,sodium or potassium and 2 when M is magnesium and m, R₁ and R₂ are thesame as defined above.

It is not necessary for the present mixed metal catalysts that bothmetals contain the same alkoxide or carboxylate moieties. For example,if aluminum and alkali metal carboxylates are employed they can bederived from different carboxylic acids. It is also possible andsometimes advantageous to employ an alkali metal alkoxide with analuminum carboxylate or, conversely, an aluminum alkoxide can be usedwith an alkali metal carboxylate.

Especially useful alkoxides for the mixed metal catalysts of thisinvention are derived from conventional C₁₋₈ aliphatic monofunctionalbranched- or straight-chain alcohols or from a C₃₋₁₂ alkoxyalcohol, suchas monomethylethylene glycol, monoethylethylene glycol, ethoxydiethyleneglycol, ethoxytriethylene glycol, methoxypolyethylene glycols,ethoxypolyethylene glycols and the like. Similarly, the carboxylates ofthe aluminum, alkali metal or magnesium are typically derived from thesame or different branched- or straight-chain aliphatic (fatty) acidswhich can contain olefinic unsaturation, benzoic acid or C₁₋₈ alkylsubstituted benzoic acid.

The mixed metal catalyst is obtained by combining the above-describedaluminum compound(s) and lithium, sodium, potassium or magnesiumcompound(s) in the prescribed molar proportions. This can beaccomplished by adding the aluminum compound and alkali metal ormagnesium compound to the reactor as such or these compounds can bereacted prior to addition to the polymerization vessel to form doublemetal salts. When the components of the mixed metal catalyst arecombined prior to introduction into the reactor, the components may bephysically admixed or, depending on the particular components and theconditions employed, partially or completely reacted. This isaccomplished with agitation, preferably under a nitrogen atmosphere, andin the absence of moisture. Where the catalyst components are reactedprior to introduction to the reactor, the resulting mixed metal salt,which is also an effective depolymerization catalyst for the process,will vary in its composition depending on the nature and molar ratio ofthe components and the conditions employed. In some instances, such aswhere an alkoxide of aluminum is reacted with an alkali metalcarboxylate, the resulting double metal salt may have entirely differentphysical and chemical characteristics than either of the components. Forexample, both metal components may be solids whereas the resulting mixedmetal salt obtained upon heating will be a liquid. This feature can beadvantageous in that it facilitates handling and introduction of thecatalyst to the depolymerization reactor. The ultraviolet spectra andabsorbtivity of the mixed metal reaction products differ from what onewould obtain from a simple mixture of the reactants. The double metalsalts obtained by reacting the aluminum carboxylate or alkoxide with thealkali metal alkoxide or carboxylate correspond to the general formulaAl M_(a) (OC_(m) H_(2m) R₁)_(b) (OOCR₂)_(c) where m, R₁ and R₂ are thesame as identified above, M represents the alkali metal, a is an integerfrom 1 to 3, b and c are integers from 0 to 6 and b+c=a+3. In anespecially useful embodiment a is equal to 1 or 3.

Particularly advantageous results are obtained using double metal saltsobtained by reacting essentially equimolar amounts of the aluminumcompound and alkali metal compound. Such mixed metal salts have theformula Al M (OC_(m) H_(2m) R₁)_(d) (OOCR₂)_(e) where M is lithium,sodium or potassium, d and e are integers from 0 to 4, and d+e=4.Especially useful mixed metal salts are obtained when M is sodium orpotassium and d=3, e=1 or d=4, e=0.

The manner in which the depolymerization is carried out, i.e., whetherthe process is conducted as a batch, continuous or semi-continuousoperation, will influence the amount and type of mixed metal catalystused and the reaction conditions employed for the process. As hasalready been indicated the depolymerization can be carried out inconventional process equipment adaptable to removal of the macrocyclicproducts formed during the course of the reaction by vacuum distillationor in equipment such as that described in U.S. Pat. No. 4,165,321,capable of continuous or semi-continuous operation. If the process isconducted in accordance with the latter procedure and the mixed metalcatalyst is added continuously or incrementally throughout the course ofthe depolymerization.

The macrocyclic compounds obtained in accordance with the presentimproved process are primarily useful in cosmetic applications. Theyimpart desirable fragrance properties and/or enhance the fragrancecharacteristics of other compounds combined therewith. For example, thecyclic esters and ether-esters, lactones and ether-lactones have utilityin detergents (heavy duty and regular laundry), soaps (bar soaps, dishsoaps and specialty beauty soaps), fabric softeners, paper products,personal care products (bath oils, shampoos, hair rinses, deodorants,shaving creams and mouthwashes), and as fine fragrance components forperfumes, perfume oils, perfume fixatives, colognes, aftershave lotionsand the like. Products obtained by the present improved process areparticularly adaptable to applications where heavy metal residues cannotbe tolerated.

The following examples illustrate the invention more fully PG,15 but arenot intended to limit the scope thereof. In these examples, all partsand percentages are on a weight basis unless otherwise indicated.

EXAMPLE I

Preparation of Polyester: Poly(ethylene brassylate) was prepared bycharging to a top-agitated resin kettle fitted with a distillation headand condenser 109 parts dimethyl brassylate and 30.5 parts polymer gradeethylene glycol. About 2.3 percent, based on the dimethyl brassylate,methyl esters of a mixture of C₁₆₋₂₂ fatty acids was included as thechain terminator. A supported titanium catalyst (0.08 part), preparedfrom tetraisopropyl titanate and a naturally acidic montmorillonite clayin accordance with the teaching of U.S. Pat. No. 4,032,550, was thenadded to the reaction mixture under a positive pressure of nitrogen andheating begun. When the temperature of the reaction mixture reachedabout 180° C. methanol began distilling from the reaction mixture andwas collected. After most of the methanol was removed and thetemperature increased to about 195° C.-205° C., a vacuum of 2 in. Hg wasapplied and increased slowly to 30 in. Hg. Samples were periodicallyremoved from the reactor for analysis and after about 11 hours thereaction mixture had an acid value of 0.1 and hydroxyl value of 15.3.Heating was terminated at this point, the reaction mixture cooled toabout 180° C. and the vacuum broken with nitrogen. The high molecularweight poly(ethylene brassylate), viscosity 117 centistokes at 210° C.,was filtered to remove the supported titanium catalyst.

A double metal salt was prepared by heating 75 parts aluminumisopropoxide (melting point 115.5° C.), 115 parts potassium stearate(melting point >260° C.), and 160 parts diethylene glycol monoethyletherat 185° C. until essentially all of the isopropyl alcohol was distilledfrom the reaction mixture. The resulting double metal salt KAl(OC₂ H₄OC₂ H₄ OC₂ H₅)₃ (OOC₁₇ H₃₅) was a homogeneous waxy solid melting overthe range 85° C.-95° C. Elemental analysis of the product confirmed thepresence of 5.3 percent potassium and 3.6 percent aluminum. The doublemetal salt was also prepared by the reaction of essentially equal molaramounts of tri(ethoxyethoxyethyl) aluminate and potassium stearate.

Following the procedure of U.S. Pat. No. 4,165,321, poly(ethylenebrassylate) was depolymerized utilizing the double metal salt as thecatalyst. For the depolymerization, 1.36 weight percent KAl(OC₂ H₄ OC₂H₄ OC₂ H₅)₃ (OOCC₁₇ H₃₅) was dissolved in the polyester and the mixturetransferred to a stainless steel holding tank maintained at 150° C. withagitation. From this tank the polyester was continuously metered into anelectrically heated stainless steel inverted vertical cone reactorfitted with two conical, helicoidal blades whose axes coincide with thecone axes of the bowl and which intermesh as they rotate in oppositedirections to provide top-to-bottom mixing throughout the total volumeof the reaction mixture. The blades were positioned within the reactorso that the maximum blade-to-wall clearance (distance between the bladesand the interior surface of the reactor) was about 0.25" and driven witha high torque motor at about 20 rpm. The reaction temperature wasmaintained between 330° C. and 360° C. at a vacuum of about 1-5 mm Hg.Ethylene brassylate was continuously distilled from the reactor and therate of addition of the polyester containing the mixed metal catalystadjusted as necessary to maintain the proper material balance. The yieldof crude ethylene brassylate produced in this manner was 83.6 percent.

EXAMPLE II

To demonstrate the versatility of the present process, poly(ethylenebrassylate) was depolymerized in accordance with the procedure describedin U.S. Pat. No. 2,092,031. Seventy-five grams of the polyester and 2grams (2.66 weight percent) of the double metal salt of Example I werecharged to a glass reaction vessel equipped with a take-off condenser.The mixture was heated to 200° C. with agitation until the mixed metalcatalyst was thoroughly blended into the polymer. The reactiontemperature was then increased and maintained at 320° C. at a pressureof 0.1-0.5 mm Hg. After the vapor temperature and distillate take-offstabilized, the distillate rate was recorded. Crude ethylene brassylatewas obtained at a rate of 40 mls/hour (measured during the first hour).After about 2 hours the reaction was essentially complete as evidencedby a sharp reduction in the distillation rate, however, heating wascontinued for two additional hours to insure completion of thedistillation. The yield of ethylene brassylate (crude) was 89.7 percent.

EXAMPLE III

To demonstrate the improved yields and increased reaction rates obtainedutilizing the mixed metal catalysts of this invention, batchpolymerizations were identically conducted using (a) a mixed metalcatalyst comprised of aluminum stearate and sodium stearate (1.1 molarratio), (b) aluminum stearate catalyst, and (c) lead stearate catalyst.These reactions were conducted in accordance with the procedure employedin Example II utilizing 74 grams poly(ethylene brassylate) and 0.5 molepercent of the catalyst. Reactions were carried out at 310°-320° C. and0.1-0.5 mm Hg for four hours. The amount of distillate (crude ethylenebrassylate) recovered was recorded after the first hour of reaction.With the mixed metal catalyst, 45 mls ethylene brassylate was obtainedafter one hour and the overall yield was 95.9 percent. With the aluminumstearate, 36 mls crude ethylene brassylate was obtained in the firsthour and the overall yield was only 78 percent. Using lead stearate only25 mls distillate was obtained after one hour and the yield of crudeethylene brassylate was 69.1 percent.

EXAMPLE IV

A mixed metal catalyst comprised of aluminum stearate and lithiumstearate (molar ratio 1:1) was used for the depolymerization. For thereaction aluminum stearate (1.09 gram) and lithium stearate (0.36 gram)were blended in 70 grams poly(ethylene brassylate) at 200° C. Thetemperature was then raised to 314° C. while maintaining a vacuum of0.05-0.1 mm Hg. Ethylene brassylate was obtained (40 mls during thefirst hour) in an 88.9 percent yield. Of the ethylene brassylaterecovered, 90 percent of the product was obtained after 2 hours.

EXAMPLE V

A mixed metal catalyst comprised of 0.40 gram potassium stearate and1.09 gram aluminum stearate (molar ratio 1:1) was employed at a 2.1weight percent level to depolymerize poly(ethylene brassylate) at atemperature of 316° C. and pressure of 0.10-0.15 mm Hg. 88.7 Percentyield crude ethylene brassylate containing less than 3 ppm aluminum andonly 1.2 ppm potassium was obtained. In a similar manner, ethylenebrassylate was produced using the same level of a mixed metal catalystcomprised of 0.74 gram magnesium stearate and 1.09 gram aluminumstearate.

EXAMPLE VI

Mixed metal catalysts comprised of potassium stearate and aluminumstearate were utilized to depolymerize poly(ethylene brassylate). Themolar ratios of catalyst components were varied from 3:1 to 1:10(potassium stearate:aluminum stearate). Reaction conditions and percentyield ethylene brassylate are provided below for each of the catalysts.

    ______________________________________                                        K Stearate:                   Reaction                                        Al Stearate                                                                            Wt. %    Reaction    Press.                                          (mole ratio)                                                                           Catalyst Temp. (°C.)                                                                        (mm Hg)                                                                              % Yield                                  ______________________________________                                        3:1      3.3      320         0.5    89.7                                     3:1      6.6      316         0.2    78.1                                     1:3      1.7      314         0.3    82.2                                      1:10    14.5     320         1.5    70                                       ______________________________________                                    

Excellent rates of reaction based on distillation data obtained duringthe first hour of reaction were observed for all of the above-reactions.

EXAMPLE VII

Aluminum tripelargonate, obtained by reacting 0.5 mole aluminumisopropoxide and 1.5 mole pelargonic acid at 120° C., was combined withan equimolar amount, based on aluminum, of potassium stearate and theresulting mixed metal catalyst (1.7 weight percent) charged to a reactorwith 76 grams poly(ethylene brassylate). The depolymerization wasconducted in the usual manner. Ethylene brassylate was obtained at arate of 42 mls/hour and yield of 89.3 percent.

EXAMPLE VIII

A mixed metal catalyst comprised of potassium brassylate and aluminumstearate (1:1 molar ratio of K:Al) was employed for the depolymerizationof poly(ethylene brassylate) at a 1.8 weight percent level. An 81.6percent yield of ethylene brassylate was obtained. Comparable yields areobtained when this mixed metal catalyst is used for the depolymerizationof poly(ethylene sebacate) and poly(3-oxa-pentamethylene azelate).

EXAMPLE IX

Sodium brassylate (0.33 gram) and aluminum stearate (1.09 gram) wereadded to 70 grams poly(ethylene brassylate) and the mixture heated at200° C. until a homogeneous viscous mass was obtained. The molar ratioof sodium to aluminum was 2:1. The temperature was then increased to312° C. and the pressure reduced to 0.3-0.5 mm Hg. The depolymerizationreaction was complete in about 3 hours and 88.1 percent yield ethylenebrassylate was obtained.

EXAMPLE X

A mixed metal catalyst was prepared by heating 0.05 mole powderedaluminum isopropylate (melting point 118° C.), 0.05 mole potassiumstearate and 0.15 mole ethyl cellusolve (HOC₂ H₄ OC₂ H₅) at 140° C.while removing the theoretical amount of isopropanol. Five-tenths molepercent of the resulting high melting (melting point >200° C.) doublemetal salt AlK(OC₂ H₄ OC₂ H₅)₃ (OOCC₁₇ H₃₅) was used to catalyze thedepolymerization of an acid-terminated poly(ethylene brassylate) (AV<10;OHV<10) at 320° C. and 0.1 to 0.5 mm Hg. Forty-two mls crude ethylenebrassylate was distilled from the reaction vessel during the first hourand the overall yield of the ethylene brassylate was 82.4 percent.

EXAMPLE XI

Repeating Example X, a double metal salt was prepared except that sodiumstearate was substituted for the potassium stearate and the ethylcellusolve was replaced with diethylene glycol monoethyl ether. Theresulting double metal salt NaAl(OC₂ H₄ OC₂ H₄ OC₂ H₅)₃ (OOCC₁₇ H₃₅) wasused as the catalyst for the continuous depolymerization ofpoly(ethylene brassylate) in accordance with the procedure andconditions of Example I. Ethylene brassylate was continuously producedand distilled from the reactor at a rapid rate and the overall yield was73.2 percent. Comparable results are obtained using the double metalsalt NaAl(OC₂ H₄ OC₂ H₅)₃ (OOCC₆ H₅) obtained by the reaction of sodiumbenzoate and aluminum tricellusolve (Al(OC₂ H₄ OC₂ H₅)₃).

EXAMPLE XII

A mixed metal compound of the formula NaAl(OCH₂ CH₂ OCH₃)₂ (O(CH₂)₆CH₃)₂, and identical to that obtained by combining sodium heptoxide withheptyl di(methoxyethyl) aluminate, was prepared by adding 0.25 molesodium bis-2-methoxyethoxy aluminum hydride (70% solution in benzene) to0.5 mole heptanal with cooling over a two hour period. The double metalsalt NaAl(OC₂ H₄ OC₂ H₅)₃ (OOCC₆ H₅), was recovered as a viscous liquidby evaporation of the solvent. 0.46 Grams of the mixed sodium-aluminumalkoxide catalyst was employed to depolymerize 70 grams poly(ethylenebrassylate) at 310°-314° C. and 0.15-0.3 mm Hg. About 85 percent yieldwas obtained in two hours. Useful mixed metal alkoxide catalysts arealso prepared following the procedure described in U.S. Pat. No.3,852,309.

EXAMPLE XIII

A mixed metal catalyst comprised of aluminum isopropoxide and sodiummethoxide (1:1 molar ratio) was utilized to depolymerize poly(ethylenebrassylate). The mixed metal catalyst was employed at a 0.48 weightpercent level. Ethylene brassylate was obtained at a rate of 44.5 mlsper hour (based on the amount collected during the first hour of thereaction) and the overall yield at the end of the four hours was 80percent.

EXAMPLE XIV

The ability to depolymerize different polyester compositions to obtain avariety of useful macrocyclic compounds is demonstrated by this examplewherein a mixed metal catalyst was employed for the preparation ofethylene dodecanedioate. For this reaction the catalyst was a doublemetal salt KAl(OC₂ H₄ OC₂ H₄ OC₂ H₅)₃ (OOCC₁₇ H₃₅) (melting point 85°C.-95° C.; 5.3 percent K, 3.6 percent Al) obtained by heating equimolaramounts of aluminum tricarbitol (Al(OCH₂ CH₂ OCH₂ CH₂ OC₂ H₅)₃) andpotassium stearate. The catalyst was used at a 1.3 weight percent levelin 70 grams poly(ethylene dodecanedioate). The mixture was heated to325° C. under reduced pressure (1 mm Hg). About 75 percent conversion ofthe polyester to cyclic product was achieved in one hour. Eighty-sixpercent yield ethylene dodecanedioate was achieved. Comparable resultsare obtained using a polyester derived from diethylene glycol.

EXAMPLE XV

To 50 grams of the polyester of 15-hydroxypentadecanoic acid was added2.0 grams of the mixed metal catalyst of Example XIV KAl(OC₂ H₄ OC₂ H₄OC₂ H₅)₃ (OOCC₁₇ H₃₅) and the mixture heated to 320° C. at 0.8-1.0 mmHg. Heating was terminated after four hours during which time 43.85grams pentadecanolide (87.7 percent yield) was obtained. Anether-lactone is produced when a polyester prepared from12-oxa-15-hydroxypentadecanoic acid is depolymerized in a similarmanner.

EXAMPLE XVI

An alcohol terminated polyester of low acid and hydroxyl value wasobtained by reacting dimethyl brassylate, ethylene glycol and cetylalcohol (0.04 mole per mole dimethyl brassylate). Seventy grams of theresulting polyester was combined with the double metal salt of ExampleXIV (1.36 weight percent) and the mixture heated under reduced pressureto effect depolymerization and formation of the cyclic diester product.Depolymerization proceeded at a rapid rate with no difficulty and 52.9grams ethylene brassylate was recovered. In an identical manner, apolyester terminated with an aromatic monocarboxylic acid(p-decyloxybenzoic acid) was depolymerized and 53.7 grams ethylenebrassylate obtained.

EXAMPLE XVII

NaAl(OCHCH₃ CH₂ CH₃)₄ was prepared by refluxing 24.7 grams aluminumtri-sec-butoxide (liquid at 25° C.), 5.4 grams sodium methoxide (meltingpoint >300° C.) and 20 grams sec-butyl alcohol while removing methanolvia a fractionating column. When the theoretical amount of methanol wasremoved, the temperature was raised to remove excess sec-butyl alcoholand recover the NaAl(OCHCH₃ CH₂ CH₃)₄ (melting point >260° C.; 6.7percent Na; 7.9 percent Al). A vacuum was applied to the system duringthe final stages of the alcohol removal. The double metal salt was usedfor the depolymerization of poly(ethylene brassylate) in accordance withthe procedure of Example I. While some of the catalyst remainedundissolved in the polyester, elemental analysis of both the undissolvedcatalyst and soluble catalyst (recovered from the polyester) wereidentical. A high yield of ethylene brassylate was obtained whilemaintaining a good reaction rate.

EXAMPLE XVIII

The double metal salt NaAl(OC₂ H₄ OCH₃)₄ was prepared following theprocedure of Example XVII by reacting 24.7 grams aluminumtri-sec-butoxide, 5.4 grams sodium methoxide and 30 grams methylcellusolve. The double metal salt had a melting point >260° C.,contained 6.6 percent Na and 7.7 percent Al, and was an effectivecatalyst for the depolymerization of poly(ethylene brassylate). Thedouble metal salt was also obtained by reacting sodium 2-methoxyethoxide(melting point >250° C.) with aluminum tri(2-methoxyethoxide), a viscousoil at 25° C.

EXAMPLE XIX

In accordance with the general procedure described above, a double metalsalt was prepared by heating 20.5 grams aluminum isopropylate, 16.2grams sodium methoxide and 70 grams sec-butyl alcohol. During theheating, methanol, isopropanol and excess sec-butyl alcohol wereconsecutively removed from the reaction mixture as the temperature wasincreased. A vacuum was applied during the final stripping stages. Thedouble metal salt AlNa₃ (OCHCH₃ CH₂ CH₃)₆ was a waxy solid melting at50°-60° C., contained 12.9 percent Na and 5.1 percent Al, and was aneffective catalyst for the depolymerization of poly(ethylenebrassylate).

EXAMPLE XX

An effective mixed metal depolymerization catalyst was obtained byreacting 24.7 grams aluminum tri-sec-butoxide, 32.3 grams potassiumstearate and 100 grams propionic acid. The reaction mixture was heatedwhile removing sec-butyl alcohol and sec-butyl propionate formed in thereaction mixture. Finally, the excess propionic acid was stripped undervacuum to obtain the KAl(OOCC₁₇ H₃₅)(OOCC₂ H₅)₃ salt (meltingpoint >300° C.; 14.0 percent K, 9.4 percent Al). The double metal saltwas employed at 0.55 weight percent level for the depolymerization ofpoly(ethylene brassylate) in accordance with the procedure of Example Iand ethylene brassylate was obtained in good yield.

I claim:
 1. A process for the production of macrocyclic compounds having8 to 20 carbon atoms in the ring and selected from the group consistingof ##STR8## where R' is a bivalent aliphatic hydrocarbon radical having1 to 16 carbon atoms, R" is a saturated bivalent aliphatic hydrocarbonradical having from 2 to 12 carbon atoms, R'" is a bivalent aliphatichydrocarbon radical having from 6 to 18 carbon atoms and x is an integerfrom 1 to 4, by thermal depolymerization of the corresponding linearpolyester which comprises heating the polyester at a temperature from200° C. to 400° C. and pressure less than 50 mm Hg in the presence of0.01 percent to 20 percent by weight, based on the polyester, of adouble metal salt of the formula

    AlM.sub.a (OC.sub.m H.sub.2m R.sub.1).sub.b (OOCR.sub.2).sub.c

where M is lithium, sodium or potassium, R₁ is hydrogen or an alkoxy orpolyalkoxy radical having from 1 to 16 carbon atoms, R₂ is a C₂₋₂₂alkyl, phenyl or substituted-phenyl having 7 to 20 carbon atoms, m is aninteger from 1 to 22, a is an integer from 1 to 3, b and c are integersfrom 0 to 6 and b+c=a+3.
 2. The process of claim 1 where a is equalto
 1. 3. The process of claim 2 wherein m is an integer from 2 to 12, R₁is hydrogen, methoxy, ethoxy, di-, tri- or tetra-ethoxy, R₂ is a C₈₋₁₈alkyl, phenyl or substituted-phenyl wherein the substituent is an alkyl,alkoxy or polyalkoxy group.
 4. The process of claim 4 where the doublemetal salt is present in an amount from 0.1 to 10 weight percent, basedon the weight of the polyester, and corresponds to the formula

    AlM(OC.sub.m H.sub.2m R.sub.1).sub.d (OOCR.sub.2).sub.e

where M is sodium or potassium, d and e are integers from 0 to 4 andd+e=4.
 5. The process of claim 4 where d=3 and e=1.
 6. The process ofclaim 5 wherein the depolymerization is carried out at a temperature inthe range 250° C. to 360° C. and pressure of 10 mm Hg to 0.01 mm Hg. 7.The process of claim 6 wherein the depolymerization is conducted as acontinuous or semi-continuous operation.
 8. The process of claim 7wherein the macrocyclic compound is ethylene brassylate.
 9. The processof claim 7 wherein the macrocyclic compound is pentadecanolide.
 10. Theprocess of claim 4 where d=4 and e=0.
 11. The process of claim 10wherein the depolymerization is carried out at a temperature in therange 250° C. to 360° C. and pressure of 10 mm Hg to 0.01 mm Hg.
 12. Theprocess of claim 11 wherein the depolymerization is conducted as acontinuous or semi-continuous operation.
 13. The process of claim 12wherein the macrocyclic compound is ethylene brassylate.
 14. The processof claim 12 wherein the macrocyclic compound is pentadecanolide.
 15. Theprocess of claim 1 where a is equal to
 3. 16. The process of claim 15wherein m is an integer from 2 to 12, R₁ is hydrogen, methoxy, ethoxy,di-, tri- or tetra-ethoxy, R₂ is a C₈₋₁₈ alkyl, phenyl orsubstituted-phenyl wherein the substituent is an alkyl, alkoxy orpolyalkoxy group.
 17. The process of claim 16 wherein the double metalsalt is present in an amount from 0.1 to 10 weight percent, based on theweight of the polyester, and the depolymerization is carried out at atemperature in the range 250° C. to 360° C. and pressure of 10 mm Hg to0.01 mm Hg.
 18. The process of claim 17 wherein the depolymerization isconducted as a continuous or semi-continuous operation.
 19. The processof claim 18 wherein the macrocyclic compound is ethylene brassylate. 20.The process of claim 18 wherein the macrocyclic compound ispentadecanolide.